SUMMARY OF WORK: We use the transgenic Big Blue system to study gene mutations in vivo. Both the lacI and the lambda-cII genes are present in Big Blue mice and rats allowing for comparative in vivo mutagenesis studies. We have characterized lacI mutations in the liver of Big Blue mice following treatment with B[a]P followed by a partial hepatectomy. Both GC>TA and GC>CG transversions were found to be significantly elevated at hepatectomy and at sacrifice as compared to untreated control animals. These data suggest that BPDE adducts at guanine and adenine are primarily responsible for gene mutations in vivo following B[a]P treatment. In addition, we have derived primary Big Blue fibroblast mouse and rat cell strains that allow for direct in vitro comparisons of mutational and cytogenetic - transgenic in vivo mutation Big Blue spontaneous mutation cII lacI gene-tox